This invention relates to a unique backset adjustment for latch constructions of the type normally used in doors and the like. More particularly, this invention relates to a preferred bayonet joint backset adjustment which is installed in each of the casing and bolt of such latch construction and is conveniently operable with far greater ease than has heretofore been possible. Thus, with minimum preplanned manipulation, it is possible to increase or decrease the backset distance of the stationary casing and to conform the movable bolt to such backset change, thereby adapting the overall latch construction to various backset measurements.
With latch constructions of the type for use with doors and the like, the backset measurement thereof is that distance between the forward extremities of the stationary casing longitudinally rearwardly to the transverse axis about which the latch operator moves for extending and retracting the bolt of the latch construction. Such measurement or measurements have, for the most part, been standardized by the industry. With such standardization, it is known when a latch construction is purchased that in a usual installation, the backset measurement will be a standard amount and from a practical standpoint, his measurement will be calculated from the forward exposed surface of the latch mounting face plate which, in effect, is the forward extremity of the stationary frame or casing. Again in a usual installation, the face place is recessed in the door edge with the front surface of the face plate aligned with the door edge so that in most cases, the backset measurement is also the distance from the door edge to the axis of the latch operator.
In the past years, the most prevalent backset has been standardized at two and three eighths inches so that it has normally been known prior to latch construction installation what the backset measurement would be, thereby permitting standardized original installation and a high degree of interchangeability between various latch constructions. It is true that there have been a few "special" latch constructions having "special" backset measurements, but these have always been considered different and of no overall consequence, except requiring individual considerations for proper installation. However, more recently a greater and greater percentage of latch constructions are being produced with a greater backset measurement for various reasons, including the provision of greater longitudinal length for greater bolt throw, that is, the longitudinal distance that the bolt is moved between retracted and extended position, in order to, in turn, provide increased security.
Therefore, an increased second backset measurement standard has been now adopted by the industry, such second standard being two and three quarters inches, three eighths inches greater than the previous first standard backset. Most manufacturers of latch constructions have satisfied this demand for the alternate two backset measurements by producing and marketing two different and distinct models of many of the latch constructions. One model has a backset measurement of two and three eighths inches to satisfy the demand for the old standard backset, while the other model has the new standard backset of two and three quarters inches, all of which is relatively costly in view of the need for manufacturing multiple models.
Thus, there is a distinct want and need in the industry for single models of latch constructions which are relatively quickly and easily selectively adjustable between the two standard backset measurements, that is, between two and three eighths inches and two and three quarters inches. Furthermore, such adjustability must be of a relatively simple nature for preforming the adjustment manipulation. Latch construction installation is frequently performed by expert workman well versed in the latch construction field and to them, adjustment simplicity may not be of maximum consequence, but latch construction installation is also performed in an equal, if not greater, number of instances by ordinary homeowners that are not trained in the latch construction field and for them, adjustment simplicity is of maximum importance.